The present invention relates to a vehicle speed control system for controlling a vehicle speed, and more particularly to a control system which controls a vehicle so as to automatically cruise at a set vehicle speed.
Japanese Patent Provisional Publication No. (Heisei) 11-314537 discloses a vehicle speed control system which controls a vehicle speed so that an actual lateral acceleration of the vehicle does not become greater than a preset lateral acceleration.
This control system is arranged to decelerate the vehicle from a target vehicle speed at a predetermined vehicle-speed variation (acceleration/deceleration) which maintains the actual lateral acceleration below a preset value. However, when the preset value of the deceleration (acceleration) is set at a small value adapted to a high speed traveling and when the vehicle travels at a low vehicle speed, the vehicle stability is degraded due to the vehicle motion characteristics under a low speed traveling condition. More specifically, since the natural frequency of a lateral motion of the vehicle is high under a low speed traveling condition, that is, since a steering response of the vehicle is quick under the low speed traveling condition, the lateral acceleration of the vehicle tends to become large and therefore the vehicle stability tends to be degraded. On the other hand, when the preset value of the deceleration (acceleration) is set at a large value adapted to a low speed traveling and when the vehicle travels at a high vehicle speed, the large deceleration of the vehicle impresses a strange feeling to a driver.
It is therefore an object of the present invention to provide an improved vehicle speed control system which ensures a vehicle stability during the deceleration of the vehicle without impressing a strange feeling to a driver even if the vehicle travels at any vehicle speed.
Another object of the present invention is to provide a vehicle speed control system which can decides whether the vehicle is traveling a curved road and varies the variation (acceleration/deceleration) of a command vehicle speed so as to fit with a drive feeling during a constant vehicle speed cruise control.
A vehicle speed control system according to the present invention is for a vehicle and comprises a lateral acceleration sensor which senses a lateral acceleration of the vehicle, a vehicle speed sensor which senses a vehicle speed of the vehicle, a target vehicle speed setting device for setting a target vehicle speed, a drive system which generates drive force of the vehicle, and a controller connected with the lateral acceleration sensor, the vehicle speed sensor, the target vehicle speed setting device and the drive system. The controller is arranged to calculate a correction quantity based on the lateral acceleration and the vehicle speed to calculate a command vehicle speed on the basis of the vehicle speed, the target vehicle speed, a variation of the command vehicle speed, and the correction quantity, and to control the drive system to bring the vehicle speed closer to the command vehicles speed.
In addition to the above aspect, the controller according to the present invention may be further arranged to determine whether the vehicle is traveling on a curved road, and to determine the variation of the command vehicle speed at the time after the traveling on the curved road is terminated, on the basis of one of a curve-terminated vehicle speed at the time when the curved road traveling is terminated and a start-end deviation between the vehicle speed at the time when the vehicle starts traveling on a curved road and the vehicle speed at the time when the curved road traveling is terminated.